There is known a wireless communication system in which a base station communicates with a mobile station via a relay station. FIG. 1 is a schematic diagram of a conventional system including a base station, a relay station, and a mobile station. As illustrated in FIG. 1, the system includes a base station BS, a relay station RS, and a mobile station MS. There may be plural base stations BS, relay stations RS, and mobile stations MS.
The section between the base station BS and the relay station RS is a first wireless section, and the section between the relay station RS and the mobile station MS is a second wireless section. The first wireless section and the second wireless section have propagation qualities (for example, CQI: Channel Quality Indicator) that are independent of each other, and have different propagation qualities. Therefore, the respective wireless sections perform propagation control with the use of different control channels.
In a communication system in which communications are performed via a relay station, in order to implement the optimum scheduling in each wireless section, resource block assignment information is transmitted in each wireless section. The base station generates resource block assignment information for each of the first wireless section and the second wireless section. Accordingly, in the first wireless section, first resource block assignment information of the first wireless section and second resource block assignment information of the second wireless section are both transmitted.
The base station reports the resource blocks to be used to each mobile station, by transmitting the resource block assignment information indicating which resource blocks are assigned to each mobile station.
The resource block assignment information is in a bitmap format. Therefore, the resource block assignment information is to include the same number of bits as the number of resource blocks. FIG. 2 illustrates the resource block assignment information according to a conventional bitmap format. For example, resource blocks are assigned in units of resource block groups each including four consecutive resource blocks. In the case of a band of 20 MHz, as illustrated in FIG. 2, there are 100 resource blocks divided into 25 resource block groups. In this case, the resource block assignment information is to have 25 bits. In the following, a resource block group is simply referred to as a resource block.
Patent document 1: WO2006/098273
As described above, in the first wireless section in the wireless communication system including a relay station, the resource block assignment information of the first wireless section and the resource block assignment information of the second wireless section are transmitted. The resource block assignment information includes many bits, and therefore the load in the control channel is high. Accordingly, in an embodiment of the present invention, the number of bits in the resource block assignment information is reduced so that the load in the control channel is reduced.